Selective silicon nitride plasma etching

Abstract

A two step method of etching a silicon nitride layer carrying a surface oxygen film from a substrate in a plasma reactor employs the steps of (1) a breakthrough step of employing a plasma of oxygen free etchant gases to break through and to remove the surface oxygen containing film from the surface of the silicon nitride layer, and (2) a main step of etching the newly exposed silicon nitride with etchant gases having high selectivity with respect to the silicon oxide underlying the silicon nitride. The plasma etching can be performed while employing magnetic-enhancement of the etching. The plasma etching is performed in a plasma reactor comprising a low pressure, single wafer tool. Plasma etching is performed while employing magnetic-enhancement of the etching. The etchant gases include a halide such as a bromide and a fluoride in the breakthrough step. The etchant gases include an oxygen and bromine containing gas in the main step.

What is claimed is: 
     
       1. A method of etching a layer of a first material including silicon nitride coated on its surface with a film including a second material containing oxygen impurities, said method comprising the steps of: (1) first, etching said oxygen impurities in said second material from the surface of said layer of said first material using a plasma free from said second material to provide a cleaned surface of said layer of said first material, said cleaned surface being substantially free from said oxygen impurities, and   (2) second, etching said cleaned layer including said silicon nitride with a different etchant including oxygen.   
     
     
       2. A method in accordance with claim 1 wherein said second etching step includes an etchant gas and gases including said oxygen impurities. 
     
     
       3. A method of etching a structure including a substrate material with a layer of material including silicon nitride, said layer of material being in turn coated on its surface with an oxygen containing film, said method comprising the steps of: (1) first, etching said oxygen containing film from the surface of said layer using an oxygen free plasma to provide a cleaned surface on said layer, said cleaned surface being substantially free from said oxygen containing film, and   (2) second, etching said layer of material with an etchant including oxygen therein and selective to the composition of said layer of material including said silicon nitride over said substrate material.   
     
     
       4. The method of claim 3 wherein said method is performed while employing magnetic-enhancement of said etching. 
     
     
       5. The method of claim 3 wherein said method is performed in a plasma reactor comprising a low pressure, single wafer tool. 
     
     
       6. The method of claim 3 wherein said method is performed while employing magnetic-enhancement of said etching with a magnetic field b parallel to the surface of said film and said layer. 
     
     
       7. The method of claim 6 wherein said magnetic field B is rotated about said plasma reactor with said field B remaining substantially parallel to said surface of said substrate. 
     
     
       8. The method of claim 3 wherein said second etching step includes an etchant selected from a gaseous halogen or a gaseous halide. 
     
     
       9. The method of claim 9 wherein said halogen or halide is selected from the group consisting of bromines and bromides. 
     
     
       10. The method of claim 8 wherein said halogen or halide includes bromine or a bromide and fluorine or a fluoride in said first etching step. 
     
     
       11. The method of claim 10 wherein said second etching step includes an oxygen containing gas. 
     
     
       12. A method of etching a silicon nitride layer on a substrate, said substrate coated on its surface with a silicon oxide layer, coated on its surface with a silicon nitride layer, coated on its surface with an oxide or oxynitride containing film, said method comprising: performing in a plasma reactor the steps on said substrate as follows: (1) a breakthrough step of employing a plasma of oxygen free etchant gases to break through and to remove said oxide or oxynitride containing film from said surface of said silicon nitride layer wherein said etchant gases include a halogen or a halide, and   (2) a main step of etching the newly exposed surface of said silicon nitride layer with etchant gases having high selectivity with respect to said silicon oxide underlying said silicon nitride wherein said etchant gases include a halogen or a halide and an oxygen containing gas.   
     
     
       13. The method of claim 12 wherein said plasma etching is performed while employing magnetic-enhancement of said etching. 
     
     
       14. The method of claim 12 wherein said plasma etching is performed in a plasma reactor comprising a low pressure, single wafer tool. 
     
     
       15. The method of claim 14 wherein said plasma etching is performed while employing magnetic-enhancement of said etching with a magnetic field B parallel to the surface of said substrate. 
     
     
       16. The method of claim 15 wherein said magnetic field B is rotated about said plasma reactor with said field B remaining substantially parallel to said surface of said substrate. 
     
     
       17. The method of claim 12 wherein said halogen or halide is bromine or a bromide. 
     
     
       18. The method of claim 12 wherein said halogen or halide includes bromine or a bromide and fluorine or a fluoride in said breakthrough step. 
     
     
       19. A method of etching a device including a silicon oxide layer coated with a silicon nitride layer which is coated on its surface with an oxygen containing film wherein said oxygen is selected from oxygen impurities, surface oxide and oxynitride, said method comprising the steps of: (1) first, etching said oxygen containing film from the surface of said silicon nitride layer using an oxygen free plasma to provide a cleaned surface on said silicon nitride layer, said cleaned surface being substantially free from said oxide film, and   (2) second, etching said cleaned silicon nitride layer with an etchant including oxygen therein and selective to said silicon nitride over said silicon oxide in said silicon oxide layer.   
     
     
       20. The method of claim 19 wherein said method is performed while employing magnetic-enhancement of said etching. 
     
     
       21. The method of claim 19 wherein said method os performed in a plasma reactor comprising a low pressure, single wafer tool. 
     
     
       22. The method of claim 21 wherein said method is performed while employing magnetic-enhancement of said etching with a magnetic filed B parallel to the surface of said film and said layer. 
     
     
       23. The method of claim 22 wherein said magnetic field B is rotated about said plasma reactor with said field B remaining substantially parallel to said surface of said substrate. 
     
     
       24. The method of claim 19 wherein said second etching step includes an etchant selected from a gaseous halogen or a gaseous halide. 
     
     
       25. The method of claim 24 wherein said halogen or halide is selected from the group consisting of bromines and bromides. 
     
     
       26. The method of claim 24 wherein said halogen or halide includes bromine or a bromide and fluorine or a fluoride in said first etching step. 
     
     
       27. The method of claim 26 wherein said second etching step includes an oxygen containing gas.